The present invention relates to a valley detection circuit, a drive circuit, a valley detection method, and a driving method.
In a control circuit of a driver, which controls a switching power supply, the voltage at a terminal (e.g., a drain of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor)) of a switching element connected to one end of an inductor rises and falls while ringing when the energy of the inductor is discharged. There has been known a circuit which detects a timing at which the voltage has reached a valley voltage in the ringing, controls switching of the switching element according to the timing, and thereby controls turning ON/OFF of the driver. The valley voltage is a minimum value of the above voltage which falls while ringing. The ringing voltage reaches the valley voltage at a plurality of timings. The above switching is carried out at one timing of the timings provided to reach the valley voltage. Incidentally, the above switching element includes, for example, a bipolar transistor, an IGBT (Insulated Gate Bipolar Transistor), or a switching element using GaN/SiC, or the like in addition to the MOSFET.
A method using an auxiliary winding externally attached to a control circuit has been known to detect each timing provided to reach the valley voltage. Specifically, the auxiliary winding is externally attached to the control circuit in such a manner as to be able to monitor the voltage between a terminal of a switching element and a terminal of an inductor connected to the terminal thereof. The voltage of the externally attached auxiliary winding is monitored and the timing provided to reach the valley voltage is detected as a valley timing.
The mounting of a circuit for detecting the valley timing by monitoring the voltage of the auxiliary winding is relatively high in cost. Thus, a technique capable of detecting a valley timing at lower cost has been required.